JP2001117070A - Liquid crystal display control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a CCFL used for back-light not to decrease in brightness even in a cooled state at the time of starting, on a display device using back- light and a transmission type liquid crystal to be used for various information processors. SOLUTION: This liquid crystal display control device monitors a current flowing through a CCFL. Since impedance of the CCFL is dependent on its temperature and the current is small due to a high impedance in the cooled state, the control device adjusts the contrast to reduce attenuation of light by a liquid crystal device when the current is small. Or it is possible to compensate for a shortage of brightness at the time of starting the CCFL by controlling an inverter so that it increases an output voltage but decreases it as the CCFL is getting warmed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display control device using a transflective liquid crystal device, and more particularly to a liquid crystal display control device which always performs optimal brightness control in response to a temperature change due to a change in a use environment or a state. The present invention relates to a display device with excellent convenience.

[0002]

2. Description of the Related Art A transmissive liquid crystal display control device is often used as a portable information processing device such as a notebook computer or a display device connected to the information processing device. Liquid crystal display control devices have low power consumption due to their characteristics,
In addition, since a length for emitting cathode rays is not required unlike a CRT, it is suitable for thinning, and is suitable not only for a notebook type information processing device but also for a stationary type information processing device characterized by power saving and space saving. Also tend to be used more often.

Since the liquid crystal itself does not emit light, display is performed by using a backlight using a fluorescent tube (CCFL) as a light source at the back. The higher the brightness of the backlight, the easier it is to see even if the surroundings are brighter, but on the other hand, it will increase power consumption and impair the power saving features,
200N for liquid crystal display control device for information processing device
It is about IT.

[0004] In order to extend the operation time of battery-driven portable information processing devices and the recent demand for power saving,
In a range where use is not hindered, so-called power management in which operation is stopped entirely or partially is performed. If the operation of the information processing device is stopped,
When it is used again, it takes a long time until it can be operated, but the display unit has a short restart time, especially CC
Since the backlight using the FL is activated instantaneously, it is required to frequently turn off the backlight.

[0005]

The CCFL used for the backlight has a characteristic that the luminance largely depends on the temperature.
Immediately after the CCFL is turned on, the CCFL itself is in a cold state and thus darkens, and has a characteristic that the CCFL gradually warms up and the luminance increases as it is used. However, recent efforts to save energy have been demanded to reduce power consumption by turning off lights as much as possible within a range where use is not hindered. Therefore, it is desirable that the CCFL be turned off frequently, but immediately after the CCFL is turned on from the turned-off state, the display of the liquid crystal display becomes dark because the CCFL is cold.

An object of the present invention is to solve the above-mentioned problem and realize a bright and easy-to-view display even immediately after the CCFL of the liquid crystal display starts to be turned on.

[0007]

In order to achieve the above object, a liquid crystal display control device according to the present invention comprises a backlight CCF.
A current detection unit is provided in an inverter circuit for supplying power to L, and a current flowing through CCFL is monitored. The impedance of the CCFL depends on its temperature. When the CCFL is cold, the impedance is high and the current is small.
As the temperature of the CFL increases, the impedance of the CCFL decreases and the current increases. That is, the temperature of the CCFL can be estimated by detecting the current supplied by the inverter.

When the CCFL is cold, the brightness of the backlight is also low. Therefore, the contrast of the liquid crystal display portion is adjusted so that the light attenuation by the liquid crystal device is reduced. As a result, although the color becomes slightly lighter, the screen becomes relatively brighter, so that it is easy to see even in a state where the luminance is low.

In addition, when the CCFL is cold, the output voltage of the inverter is increased, and the output voltage is controlled to decrease as the CCFL warms, thereby making it possible to compensate for the lack of brightness at the time of starting the CCFL. .

In addition, when the CCFL is cold, the duty of the output of the inverter is set to 100%, and the duty is reduced as the CCFL warms up, thereby compensating for the lack of brightness at the time of starting the CCFL. Becomes

According to the present invention, a backlight CCFL is provided.
It is possible to obtain sufficient luminance immediately after turning on the display, and to increase the luminance at the start of display even if the display is turned on and off with a screen saver or the like without increasing power consumption and heat capacity during normal operation. The purpose is to secure the display device so that it is easy to see.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a liquid crystal display means comprising a transmissive liquid crystal device, a backlight means for irradiating the liquid crystal display means from the back,
The light source of the backlight means is CCFL (cold cathode ray tube)
Backlight lighting means, contrast adjusting means for adjusting the contrast of the liquid crystal display means, inverter means for supplying power for lighting the backlight means, and C constituting the backlight lighting means.
A tube current detecting means for detecting a tube current flowing through the CFL, wherein when the current value detected by the tube current detecting means is smaller than a predetermined value, control is performed such that the contrast of the liquid crystal display means is reduced. A liquid crystal display control device characterized in that, when the brightness of the backlight is insufficient at the time of starting the CCFL, the contrast is lowered and a large amount of light of the backlight is transmitted to the front surface, so that it is easy to see from the start.

According to a fourth aspect of the present invention, there is provided a liquid crystal display means comprising a transmission type liquid crystal device, a backlight means for irradiating the liquid crystal display means from behind, and a CCFL (cold cathode ray tube) using a light source of the backlight means. Backlight lighting means, inverter means for supplying electric power for lighting the backlight means, tube current detection means for detecting a tube current flowing through a CCFL constituting the backlight lighting means, and the tube current A liquid crystal display control device for controlling an output voltage of the inverter means based on current value data detected from the device. The brightness of the CCFL at the time of starting the CCFL can be increased so that it is easy to see from the start. It has the action of:

According to a sixth aspect of the present invention, there is provided a liquid crystal display means comprising a transmission type liquid crystal device, a backlight means for irradiating the liquid crystal display means from behind, and a CCFL (cold cathode ray tube) using a light source of the backlight means. Backlight lighting means comprising: inverter means for supplying power for lighting the backlight means; tube current detection means for detecting a tube current flowing through a CCFL constituting the backlight lighting means; A liquid crystal display control device comprising duty control means for on / off control of an oscillation operation, wherein the duty control means is controlled based on current value data detected from the tube current. This has the effect of increasing the brightness and making it easier to see from the start.

Hereinafter, a liquid crystal display control device according to an embodiment of the present invention will be described in detail with reference to FIGS.

(Embodiment 1) FIG. 1 is a block diagram of an inverter circuit in a liquid crystal display control device of the present invention.

Reference numeral 100 denotes an information processing apparatus, which internally includes components that constitute the information processing apparatus, such as a CPU and a MEMORY (not shown). Reference numeral 101 denotes a liquid crystal display control device.
00. 102 is an LCD which controls the brightness of the liquid crystal display, 106 is a CCFL (cold cathode ray tube) which is a light source of a backlight, and 105 is a CCF
Inverter for generating L drive voltage, 104 is a CCFL
It is a tube current detection unit that detects a current flowing through the tube.

The information processing apparatus 100 includes at least
LCDC1 for generating various signals for driving LCD
03, and a control unit 107 that outputs a signal for changing the contrast to the LCDC 103. The other circuits are included in the main body circuit 110.

When the display of the liquid crystal display control device is stopped in a key standby state or the like, the signal to the LCD 102 is also stopped, and the CCFL 106 is turned off. In this state, when an input is performed from the keyboard or the mouse to the information processing apparatus 100 of the main body, the user determines that a request to the information processing apparatus has started and resumes the display. That is, the LCDC 103
Sends a signal necessary for driving the LCD 102 to operate the LCD 102, and activates the inverter 105 to light the CCFL 106.

In the CCFL 106, when the tube is cold at the time of startup, the pressure of the mercury vapor inside is low and lower than in the normal operation. FIG. 2 is a graph showing the time transition of the starting characteristic of the CCFL. Normally, the brightness becomes almost steady in about one minute. However, when the user operates, some processing is performed, so that the user can watch the screen immediately afterward, so that sufficient brightness is required. Immediately after the CCFL is started, the impedance is so high that the current does not easily flow. Therefore, by detecting the value of the tube current detecting unit 104, it is possible to detect a state where the luminance is insufficient.

When the value of the tube current detector 104 is small,
The control unit 107 controls so as to decrease the contrast of the liquid crystal display. By reducing the contrast of the liquid crystal display, the amount of light transmitted through the LCD 102 increases, so that the entire screen becomes brighter even when the luminance of the CCFL 106 is reduced.

As a method of adjusting the contrast, the value of the data to be displayed may be increased or decreased based on the instruction of the control unit 107, or may be realized by adjusting the voltage at which the LCD 102 drives the liquid crystal. The contrast adjustment method itself may be a general method, and the description thereof will be omitted.

(Embodiment 2) FIG. 4 is a block diagram of an inverter circuit in a liquid crystal display control device of the present invention. Reference numeral 400 denotes a control IC for performing ON / OFF switching control of the inverter. 401 is an inductor, 402
Is a switching transistor. A piezoelectric transformer 403 generates a high voltage by applying a voltage converted by a switching operation and giving a vibration. The voltage boosted by the piezoelectric transformer 403 is CCF
L (cold cathode ray tube) 406. CCFL406
Is divided by a voltage dividing resistor 405 to control IC
This is fed back to 400. 404 is CCFL40
6 is a tube current detector for detecting a current flowing through the tube 6. 407
Is a capacitor for reducing the ripple of the DC power supply.

The basic operation of the inverter will be described with reference to FIG. An inverter circuit for a notebook computer operates with a DC power supply of more than ten volts as an input. Control IC4
At 00, a switching operation is performed to generate a signal that repeats on and off. When the gate signal of the switching transistor 402 becomes H level, the transistor 402 is turned on to pass the current, and when the gate signal becomes L level, the transistor 402 is turned off to cut off the current. In the on-state, a current flows through the inductor 401 to store energy, and in the off-state, the energy stored in the inductor 401 is released, so that a current flows in the opposite direction and an AC signal is generated. This AC signal is applied to the piezoelectric transformer 403. The piezoelectric transformer expands and contracts when a voltage is applied, and applies pressure to the piezoelectric element. When a pressure is applied to the piezoelectric element, a high voltage is generated, so that a high voltage for driving a CCFL (cold cathode ray tube) can be obtained.

The voltage applied to the CCFL is divided by a resistor and fed back to the control IC 400. Also CC
The current flowing in the FL is also detected by the tube current detection unit 404 and fed back to the control IC 400. Since the CCFL has an appropriate impedance while it is lit properly,
If the voltage / current applied to the CFL is within a predetermined value range, the operation is normal. By stopping,
Provides safety protection.

When the CCFL is cold at startup, the mercury vapor pressure inside the tube tends to be low and the impedance tends to be high, so that the current flowing through the CCFL decreases and the brightness of the CCFL decreases. FIG. 2 shows the time transition of the temperature and the luminance. In general CCFL, about 1 from the start
The brightness stabilizes in about a minute. FIG. 3 shows the time transition of the current flowing through the CCFL at this time.

As described above, since the luminance of the CCFL can be estimated from the value of the tube current, the CCFL can be estimated from the value of the tube current detector 404.
When the current flowing through is low, control is performed in a direction to increase the brightness.

The control IC 400 controls the output voltage by changing the switching duty. Since the peak value of the voltage applied to the piezoelectric transformer 403 is constant, the peak value of the voltage of the secondary output is also constant. Assuming that the waveform is a rectangular wave, when the peak value is constant, the average value becomes the highest when the duty is 50%, and the average value decreases regardless of the on / off duty. Therefore, when the value of the tube current detector 404 is low, the duty is controlled so as to approach 50%. Thereafter, as the temperature rises and the current flowing through the CCFL increases, the on-period decreases to 40% and 30% and becomes stable. To control. As a result, the brightness of the CCFL can be obtained immediately after the start-up, so that an easy-to-read display device can be realized.

(Embodiment 3) FIG. 5 is a block diagram of an inverter circuit in a liquid crystal display control device of the present invention.

The basic operation of switching is the same as that of the second embodiment, and a description thereof will be omitted. CC in the control IC 500
Control is performed so that a constant voltage is applied to FL. Control IC
500 is provided with a terminal for inputting an oscillation on / off signal.
When the oscillation on / off signal is turned on, the switching operation is performed and the inverter outputs the signal, and when the signal is turned off, the output is stopped.

When the repetition of ON / OFF is repeated at a period of more than ten ms, the CCFL is turned on during the ON state, and the CFL is turned off when the ON state is turned OFF.
Since the CFL is turned off, the average luminance decreases, so that luminance control can be performed. The luminance can be reduced by controlling the on / off duty and shortening the on period. In the liquid crystal display control device of the present invention, the duty of the on-period when displaying the maximum luminance during the normal operation is set to a value lower than 100%, for example, 70%.

When the information processing apparatus is started by a key input or the like from a state where the CCFL is turned off by a screen saver or the like, the CCFL is controlled to be turned on. At this time C
Since the CFL is cold, the tube current detector 404 detects a low value. When the tube current is smaller than the predetermined value, control unit 510 turns on the oscillation on / off signal so that control IC 500 turns on the CCFL with a duty of 400%.

When the CCFL 406 warms and the tube current rises, the current value detected by the tube current detection unit 504 exceeds a predetermined value.
The lighting period of L is controlled to be 70%.

In this case, the inverter circuit needs a driving capability of 400%. However, since only 70% driving is performed in a normal operation, the efficiency of 70% is sufficient in terms of thermal design, and the size can be reduced. It becomes possible. Since the brightness is increased by the current value at the start of the CCFL, a display device that is brighter and easier to see than at the start can be realized.

[0035]

As described above, according to the present invention, when the backlight of the liquid crystal display control device is controlled to be frequently turned off in order to reduce the power consumption of the information processing device, the CCFL of the backlight is reduced. Even in a state where the impedance increases due to cooling and the tube current supplied from the inverter circuit decreases, control is performed so that the drive voltage of the inverter is increased, and the tube current is increased only at the time of start-up. However, an easy-to-view display without a decrease in luminance is realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a liquid crystal display control device of an information processing device according to an embodiment of the present invention.

FIG. 2 is a graph showing the transition of luminance and temperature of CCFL over time.

FIG. 3 is a graph showing a time course of impedance and temperature of CCFL.

FIG. 4 is a block diagram of an inverter circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram of an inverter circuit according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 information processing device 101 liquid crystal display control device 102 LCD 103 LCDC 104, 404, 504 tube current detection unit 105 inverter 106, 406 CCFL (cold cathode ray tube) 107, 510 control unit 400, 500 control IC 401 inductor 402 transistor 403 piezoelectric transformer 405 Voltage divider 407 Capacitor

Claims (7)

[Claims] 1. A liquid crystal display means comprising a transmission type liquid crystal device, a backlight means for irradiating the liquid crystal display means from behind, and a backlight lighting means comprising a CCFL (cold cathode ray tube) as a light source of the backlight means. Contrast adjusting means for adjusting the contrast of the liquid crystal display means, inverter means for supplying power for lighting the backlight means, and tube current for detecting a tube current flowing through the CCFL constituting the backlight lighting means. A liquid crystal display control device, comprising: a detection unit, wherein when the current value detected by the tube current detection unit is smaller than a predetermined value, the contrast of the liquid crystal display unit is controlled to decrease. 2. The liquid crystal display control device according to claim 1, wherein the contrast adjustment unit is included in a liquid crystal control unit that generates a control signal from the data in the information processing device to the liquid crystal display unit. 3. The liquid crystal display control device according to claim 1, wherein the contrast adjusting unit is included in a liquid crystal display unit. 4. A liquid crystal display means comprising a transmissive liquid crystal device, a backlight means for irradiating the liquid crystal display means from behind, and a backlight lighting means comprising a CCFL (cold cathode ray tube) as a light source of the backlight means. Inverter means for supplying power for lighting the backlight means, and a CCF constituting the backlight lighting means.
A liquid crystal display control device, comprising: a tube current detecting means for detecting a tube current flowing through L; and an output voltage of the inverter means based on current value data detected from the tube current. 5. The control method according to claim 4, wherein the output voltage of the inverter means is increased only when the current detected by the tube current detection means is smaller than a predetermined value and only at the start of starting. The liquid crystal display control device as described in the above. 6. A liquid crystal display means comprising a transmissive liquid crystal device, a backlight means for irradiating the liquid crystal display means from behind, and a backlight lighting means comprising a CCFL (cold cathode ray tube) as a light source of the backlight means. Inverter means for supplying power for lighting the backlight means, and a CCF constituting the backlight lighting means.
L includes a tube current detecting means for detecting a tube current flowing through L, and a duty control means for turning on and off the oscillation operation of the inverter, and controlling the duty control means based on current value data detected from the tube current. A liquid crystal display control device characterized by the above-mentioned. 7. The control of the duty control means so that the output of the inverter becomes a 100% duty output only when the current detected by the tube current detection means is smaller than a predetermined value and only at the start of startup. The liquid crystal display control device according to claim 6, wherein: